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assemblages and calcification
Luc Beaufort, Michaël Grelaud
To cite this version:
Luc Beaufort, Michaël Grelaud. A 2700-year record of ENSO and PDO variability from the Californian
margin based on coccolithophore assemblages and calcification. Progress in Earth and Planetary
Science, Springer/Japan Geoscience Union, 2017, 4 (1), �10.1186/s40645-017-0123-z�. �hal-01669206�
R E S E A R C H A R T I C L E
Open Access
A 2700-year record of ENSO and PDO
variability from the Californian margin
based on coccolithophore assemblages and
calcification
Luc Beaufort
1*and Michaël Grelaud
2Abstract
The El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) account for a large part of
modern climate variability. Over the last decades, understanding of these modes of climate variability has increased
but prediction in the context of global warming has proven difficult because of the lack of pertinent and
reproducible paleodata. Here, we infer the dynamics of these oscillations from fossil assemblage and calcification
state of coccolithophore in the Californian margin because El Niño has a strong impact on phytoplankton ecology
and PDO on the upwelling intensity and hence on the ocean chemistry. Intense Californian upwelling brings water
rich in CO
2and poor in carbonate ions and coccolithophores secrete lower calcified coccoliths. Seasonally
laminated sediments of the Santa Barbara Basin are used to document ENSO variability and PDO index for the last
2700 years at a temporal resolution of 3 years. The records present the same characteristics as other PDO or ENSO
records from the same area spanning the last centuries. We are therefore confident on the value produced here for
the last 2.7 millennia. The records show important centennial variability that is equivalent to solar cycles.
Keywords: El Niño Southern Oscillation, Pacific Decadal Oscillation, Past climate variability, Santa Barbara Basin,
Solar cycles, Centennial climatic variability
Introduction
El Niño Southern Oscillation (ENSO) and its longer
lived cousin, the Pacific Decadal Oscillation (PDO)
(Zhang et al. 1997), are the primary sources of global
interannual variability. While the ENSO is related to the
interconnections between ocean and atmosphere in the
tropical eastern Pacific, the PDO is a combination of
different physical processes operating on different time
scales,
including
remote
tropical
forcing
(ENSO),
oceanic thermal inertia, and atmospheric forcing in
re-sponse to the Kuroshiyo-Oyashio dynamics (Newman
et al. 2016). Yet, their past dynamics remain poorly
understood and described. ENSO and PDO act
respect-ively at interannual and decennial scales with variable
periods ranging respectively from 2.5 to 7 years and
from 20 to 30 years (Mantua et al. 1997; Philander
1983). The impact of ENSO and PDO on the climate of
the 20
thcentury, particularly the unusual strong events
of 1982–83 and 1997–98 (El Niño) and the climate
regime shifts of 1946 and 1977 (PDO), led to a better
assessment and understanding of these cycles. However,
understanding their changing intensity and frequency
during the 21
stcentury is important issues which need
to be resolved if we want to predict how these
oscillations will be affected by new boundary conditions.
By combining recent and past marine sedimentary
archives, we aim to monitor the natural variability of
these oscillations during the past 2700 years.
The Santa Barbara Basin (SBB) is a sensitive recorder
of past climate variability (Behl and Kennett 1996;
Biondi et al. 1997; Hendy and Kennett 2000). It is an
ideal site to document past variations of ENSO and
PDO because of seasonally laminated sediments with
excellent preservation during warm periods and high
* Correspondence:beaufort@cerege.fr
1Aix Marseille University, CNRS, IRD, Collège de France, CEREGE, Avenue Louis
Philibert, BP8013545 Aix-en-Provence, Cedex 04, France Full list of author information is available at the end of the article
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
sedimentation rates (Behl and Kennett 1996; Grelaud
et al. 2009a). Located in the center of the California
Current System (CCS), the SBB is seasonally affected by
two opposite currents: the southward California Current
(CC) during late spring and summer; and the northward
Davidson Current (DC, also known as the California
Countercurrent or the California Undercurrent) during
late fall and winter. The intensity of these two currents
is modulated by the North Pacific High (NPH) and the
Aleutian Low (AL). Upwelling activity in the area is
related to the strength of the CC, as it brings deeper
waters rich in nutriment to the surface. The waters are
characterized by low pH and carbonate ion
concentra-tions (Alin et al. 2012). At interannual and decennial
scale, ENSO and PDO impact directly the intensity of
these atmospheric cells, leading to measurable variations
of CC and DC flows (Bograd and Lynn 2001; Chavez
et al. 2003). During the cold phases of ENSO or PDO
(La Niña or negative PDO), the AL is centered over the
northwest Pacific and the NPH intensifies leading to
strengthening of the CC, associated upwelling, and a
weakening of DC. The opposite occurs during warm
phases of ENSO or PDO (El Niño or positive PDO), as
the AL strengthens and moves southward over the
cen-tral Pacific, reducing the intensity of the NPH. ENSO
and PDO are modulating the strength of the upwelling
system in SBB.
The impact of ENSO and PDO in the SBB is inferred
from the interplay of the currents within the CCS whose
dynamics can be estimated by carefully analyzing fossil
assemblages of microalgae growing in the upper photic
zone: the coccolithophores (Calcihaptophycidae,
Hapto-phyta). Their productivity depends directly on the
physi-cochemical characteristics of the CCS. Coccolithophore
assemblages are very sensitive to seasonality and can be
used to diagnose changes in ENSO as evidenced in 20
thcentury records (De Bernardi et al. 2005; De Bernardi
et al. 2008; Grelaud et al. 2008). In some species or group
of species, the morphology of the scales constituting their
exoskeleton is related to physicochemical parameters of
the ocean such as temperature for their size (Bollmann
et al. 2002) or concentration in carbonate ion for their
mass (Beaufort et al. 2011). We will infer dynamics of the
upwelling with this latter parameter. We also present the
record of the relative abundances of Gephyrocapsa
ocea-nica (%GEO), a subtropical species characteristic of DC
intensity. In the SBB, its abundances are strongly
dependent of temperature associated with warm El Niño
events (De Bernardi et al. 2005; Grelaud et al. 2008).
Methods/Experimental
The data of coccolithophore assemblages and
morph-ology were extracted from two sedimentary archives
retrieved in the SBB: a multi-core was used to cover the
last 100 years (BASIN04-1MC3, 2004, 34°13.41′N, 120°
01.53′W, 588 m water depth) while a giant piston core
was used to cover the last 2.7 kyr (MD02-2503, 2002,
34°17.17′N, 120°02.17 W, 569 m water depth) (Fig. 1).
For the chronology of core BASIN04-1MC3, see Grelaud
et al. (2009b).
The chronology of the MD02-2503 combines five
14C
AMS dating and a tuning of its magnetic susceptibility to
Fig. 1 Location of IMAGES VIII core MD02-2503, BASIN 04 MultiCore 1MC3, and ODP Site 893A. The arrows represent the direction of warm (red) and cold (blue) currents and the counterclockwise circulation (black) in the Santa Barbara Basin
that of the nearby Ocean Drilling Program (ODP) Site
893A (Grelaud et al. 2009b) (Fig. 1) which combines 25
14C
dates in the Holocene (Hendy et al. 2002; Roark et al.
2003). The 3.5 uppermost meters of the MD02-2503,
repre-senting the last 2700, were sampled every 0.5 cm leading to
a resolution of ~3.6 year. The chronology of this section
has been slightly reevaluated from Grelaud et al. (2009b) by
using the age model of ODP Site 893A (Schimmelmann
et al. 2006) and its revised version (Schimmelmann et al.
2013) (Fig. 2). The synchronization between core
MD02-2503 and ODP Site 893 imposes a precision in the
chron-ology of the core MD02-2503 estimated to be around
30 years. With this chronology, the age at the core top is
around 1916. The presence at about 20 cm of many shell
debris can be attributed to the Macoma event which is
dated between 1820 and 1850 (Burke et al. 1996).
The sediment of the upper 3.5 m of Core MD02-2503
is composed in majority of hemipelagic laminated
sedi-ments (diatom nannofossil clayey silt and diatom
nanno-fossil silty clay). Eighteen millimetric to centimetric gray
layers, representing flood deposits (Behl 1995), were
observed within this interval of 3.5 m. The levels at
which those layers occur are in good agreement with
that found in ODP 893A (Schimmelmann et al. 2006).
The coccoliths in those layers are at least 10 times less
abundant than in the rest of the core. Although there is
no shift in the morphology inside and outside, these
layers have been withdrawn from this study. The
chron-ology has been established accordingly, as we consider
these layers as geological instantaneous events.
The sample preparation and analyses for coccolithophore
assemblages are the same as for Grelaud et al. (2009a): smear
slides were prepared according to standard procedure and
were analyzed with an automated system of coccoliths
recog-nition (SYRACO, Beaufort and Dollfus 2004; Dollfus and
Beaufort 1999). An average of 600 (BASIN04-1MC3) and
900 (MD02-2503) individuals was counted in each samples
and 6 species represented more than 96% of the assemblages:
Emiliania huxleyi, Florisphaera profunda, Gephyrocapsa
ericsonii, Gephyrocapsa muellerae, Gephyrocapsa oceanica,
and Helicosphaera carteri.
The average mass of calcite of the coccoliths belonging
to the Noelaerhabdaceae family was precisely estimated
by using the birefringence properties of the calcite when
viewed in cross polarized light and by following the
method described by Beaufort (2005).
Results and discussion
A Coccolithophore markers of ENSO
The high-resolution record (four samples per year)
of the coccolith assemblages present in core
BASIN04 and covering the last 100 years
(Grelaud et al.
2009b) indicates that higher relative
abundances of
G. oceanica are associated with El
Niño years (Fig.
3). This relatively warm water
species get into the Santa Barbara Basin in higher
relative abundance when the California current
relaxes (De Bernardi et al.
2005; De Bernardi et al.
2008; Grelaud et al.
2009b). The relative abundances
of this species in the sediment of the SBB can be then
used to track the occurrence of past El Niño events.
As the North Pacific Ocean is at the end of the
ocean thermohaline circulation system (Broecker
and Peng
1982), the upwelled waters in the CCS are
rich in CO
2(Feely et al.
2008). During the upwelling
season, i.e., in early spring and summer (Pennington
and Chavez
2000), surface waters are relatively cold,
rich in CO
2and nutrients, low in pH, and poor in
oxygen and carbonate ions (Alin et al.
2012). The
upwelling is intensified during La Niña and
decreased during El Niño events, and these have
strong consequences on the water chemistry of the
Santa Barbara Basin. For example, the regional
average of carbonate ion concentration was lower
during the La Niña event of 2008 ([CO
32−] =
125
μmol kg
−1) and higher during the El Niño event
of 2006 ([CO
32−] = 168
μmol kg
−1) as reported by
CalCOFI hydrographic cruises (2005
–2011)
(Alin et al.
2012).
0 5 10 15 20 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 Magnetic susceptibility (MD02-2503)Magnetic susceptibility (ODP 893)
Age (x1000 years BP)
Depth (m - ODP893 scale)
Fig. 2 Chronology of Core MD02-2503: the magnetic susceptibility of core MD02-2503 (red) (Beaufort et al. 2002) is compared to that of ODP 989 (purple) (Kennett and Ingram 1995) and 7 tie points (blue) are chosen to match the two records. Secondary magnetic susceptibility peaks indicate that this match is precise at +/−5 cm between those tie points. Some minor differences appear between the two records when susceptibility is low; those discrepancies are not used for chronology. 14C dates for MD02-2503 (light blue) and ODP 893 (green) from planktonic foraminifera. In black is the revised varved chronology based on14C date of terrestrial fossils (Schimmelmann et al. 2013)
When producing their carbonated exoskeleton,
coccolithophores are dependent on the carbonate
chemistry of the surrounding water (Beaufort et al.
2011; Langer et al.
2006; Langer et al.
2009; Muller
et al.
2012; Ridgwell et al.
2009; Riebesell et al.
2000;
Rost et al.
2008; Trimborn et al.
2007). We tested
here how the seasonal and interannual changes in
[CO
32−] induced by CCS upwelling dynamics impact
coccolithophore calcification. Using the data
published by Grelaud et al. (2009b), we studied the
coccolith mass (CM) of
Gephyrocapsa ericsonii, G.
muellerae, and Emiliania huxleyi. Gephyrocapsa
oceanica being one of the heaviest species belonging
to the Noelaerhabdaceae family, any change in
relative abundance would have a strong impact on
the average mass of the group. In consequence, the
mass of
G. oceanica was not included in order to
have two independent proxies (coccolith mass and
percentage of
G. oceanica). The differences in
coccolith mass are attributed here as the relative
abundance of the two
E. huxleyi morphotypes that
present distinct degree of calcification and that are
both abundant in this area: Winter (1985) described
in the CCS a heavy form of
E. huxleyi referred as
«warm» and a light one referred as «cold». Although
they were observed living in the same area together,
he found «difficult to relate either temperature or
salinity alone to placolith type». This early
observation by Winter (1985) fits perfectly with the
morphometric data we produced here: results show
that the coccolith mass, smoothed with a locally
weighted regression (LOESS) (Cleveland and Devlin
1988), generally increases during El Niño events
(Fig.
4). A general relation between coccolith mass
and [CO
32−] has been established (Beaufort et al.
2011) to express the importance of the ocean
carbonate chemistry on the calcification of the
Noelaerhabdaceae (the general regression line
plotted in (Beaufort et al.
2011) Fig.
1
is [CO
32−] =
20 × CM + 71.2). The mass is not considered to
produce a reliable proxy for past [CO
32−] as other
factor such as temperature, salinity, and nutriment
(e.g., Henderiks et al.
2011) may have also influence
on the mean coccolith mass. We can use here this
relation to check if the measured coccolith mass is
in agreement with some known levels of carbonate
concentration measured in SBB. In Fig.
4, the upper
right axes represent the concentration of carbonate
ions in a scale corresponding to the coccolith mass
taken from Beaufort et al. (2011). Associated with
these axes are the ranges of [CO
32−] estimated from
the CalCOFI hydrographic measurements from the
California Current System between 2005 and 2011
(Alin et al.
2012). The green box represents the
Fig. 3 Top: percentage of G. oceanica in the coccolith assemblage in black line with dots. The blue line is the record smoothed by a locally weighted regression (LOESS). Bottom: NINO3 index (black line with dots original—red smoothed (LOESS) record.) (Kaplan et al. 1998; Reynolds et al. 2002) (data available at http://iridl.ldeo.columbia.edu/). Major El Niño events are indicated by numbers, arrows, and orange bands. Minor El Niño by purple bands. (Adapted from Grelaud et al. (2009b))range obtained during the upwelling season and the
red during the no-upwelling season. The red arrow
represents the maximal value obtained during an El
Niño event and the green arrow the minimal value
obtained during a La Niña year. Those ranges are in
good agreement with the expected coccolith
mass
–[CO
32−] equivalent. Increases of coccolith mass
in the SBB can be interpreted as an increase of
[CO
32−] related to a decrease in the intensity of the
upwelling during an El Niño event.
The anthropogenic input of CO
2in the atmosphere
diffuses into the ocean from its surface. In the
California Margin, the last time the upwelled waters
were exposed to the atmosphere was 50 years ago
(Feely et al.
2008). The ocean acidification is
there-fore somehow delayed in this area and the pH is
more dependent on the upwelling activity than on
the recent increase of atmospheric CO
2. The
modu-lation of El Niño
’s by the Pacific Decadal Oscillation
appears in this record (Fig.
5): during high PDO’s
events (1925
–1945 and 1980–2000), the mass of
coccolithophores is generally higher than average
and the same is also true for secondary events
marked by red bands in Fig.
5. The imprint of El
Niño on the coccolith mass shades slightly the
match between CM and PDO at high frequency.
Although the CM and %GEO records result from
independent sources, they both increase during El
Niño events (Figs.
3
and
4). The two proxies follow
slightly differently these climate processes as each
responds also differently to other forcing (e.g.,
nutrient content, seasonal dynamics, cloud cover…).
In order to obtain a unique marker of PDO and
ENSO in SBB, we propose to combine %GEO and
CM because of their visual resemblances. Although
they are independent markers, having different units
and representing different proxies
—one diagnostic of
the dynamics of the upwelling (CM), the other of
SST (%GEO)
—their dynamics has a common
forcing that is the PDO-ENSO system. Their
com-bination will allow easier comparison with published
variables and pictures in a unique way the dynamics
of the ENSO in that region. %GEO and CM were
combined by averaging them after standardization
(subtracting their average of each variable and by
dividing them by their standard deviation. Their
sum is divided by two in order to keep the values
between
−1 and 1:
COCOC
¼
ð
ð
%GEO−mean %GEO
ð
Þ
Þ=std %GEO
ð
Þ
Þ
þ CM−mean CM
ð
ð
ð
Þ=std CM
ð
Þ
Þ
Þ=2:
This new combined marker is labeled COCOC that
stands for combined coccolith proxies. It features
the common variations of the two proxies, for
example, COCOC will increase significantly during
%GEO and CM common rise.
Fig. 4 Twentieth century records of the variability of the coccolithophore nannoflora. Top: mean mass in picogram of coccoliths belonging to the species E. huxleyi, G. ericsonii, and G. muellerae in black line with dots. The blue line is smoothed (LOESS) records. The scale on the right represents the concentration in ion bicarbonate equivalent to the coccolith mass from the relation proposed in Beaufort et al. (2011). The boxes associated with these axes are the ranges of [CO32−] between 2005 and 2011 (Alin et al. 2012). Green upwelling season, Red no-upwelling season. Red arrowhead represents the maximal value obtained during an El Niño event, and the green arrowhead the minimal value obtained during a La Niña event. Bottom: NINO3 index (black line with dots original—red smoothed (LOESS) record.) (Kaplan et al. 1998; Reynolds et al. 2002) (data available at http://iridl.ldeo.columbia.edu/). Major El Niño events are indicated by numbers, arrows, and orange bands. Minor El Niño by purple bands. (Adapted from Grelaud et al. (2009b))
B Coccolithophores, assemblages, and morphometry
during the last 2700 years
The morphometric (CM) and assemblage (%GEO)
records of coccoliths are both showing similar rapid
changes as well as a long-term decrease over the last
2700 years (Fig.
6). The polynomial regressions
presented in Fig.
6
indicate that the coccolith mass
and the relative abundance of
G. oceanica gradually
decreased from about 3.65 pg and 4% respectively
(2700 years ago) to about 3.2 pg and 1.5% between
1400 and 1800. This could be attributed to a
predominantly negative phase of the PDO; however,
as the decrease is more pronounced in %GEO than
that in CM, it more certainly results from a decrease
in sea surface temperature (SST) during that time.
Such decrease has already been documented in
many parts of the ocean including the SBB
(McGregor et al.
2015). The relation between SST
and %GEO is confirmed by the comparison, over the
last 700 years, of our results with a high-resolution
record of alkenones measured at ODP Site 893 in
the SBB (Zhao et al.
2000). Both records are
presented in Fig.
7
according to the revised
chronology (Schimmelmann et al.
2013). The
smoothed (LOESS) records reveal a common
regularity of the centennial variability in both
records (Fig.
7). The cross spectral analysis
(Blackman-Tukey) performed on the two time series
shows that the coherency between SST and %GEO
for the last 700 years is significant (
P > 0.95) at three
frequencies (1/118, 1/36, and ~1/23 years
−1) and
relatively in phase (within the chronological
constraint) between the two records (Fig.
8). The 23
year period is often reported for the PDO (Biondi
et al.
2001; Biondi et al.
1997; Minobe
1999).
Although at its lower range, the 36 year period could
be assimilated to the pentadecadal (30–70 years)
PDO variability (Minobe
1999). The significant
relation between SST and %GEO confirms that
%GEO can be used to diagnose SST evolution in the
SBB. The presence of those frequencies in the time
series shows the constant feature of the PDO over
the last 700 years. The imprint of the PDO on the
upwelling and SST of SBB confirms that it is an
important factor of SST variability in this region
(Biondi et al.
1997). Although, in some rare parts of
the records, a divergence appears: for example, in
year 450, %GEO peaks higher than CM. We do not
have explanation for those differences that reflect
the complex response of an ecological system to
climate.
Increases of CM or %
G. oceanica occur
synchronously in both records at a regular
centennial pacing (Figs.
6
and
9). The centennial
variability is well expressed and highly coherent.
The records, smoothed with a LOESS, reveal the
regularity of the centennial variability (Fig.
9). The
regular peaks of %GEO and CM covering the last
2700 year depict the alternation of sustained phases
of ENSO-like and/or PDO conditions at centennial
Fig. 5 Comparison between the mass of coccoliths of E. huxleyi, G. ericsonii, and G. muellerae (Top) and Pacific Decadal Oscillation (PDO) index (Mantua and Hare 2002). Red bands highlight periods of high PDO% G.oceanica 0 1 2 3 4 5 6 7 8 9 Coccolith mass (pg) 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 Year (CE) 500 0 500 1000 1500 2000
Fig. 6 Two thousand and seven hundred-year records of variability of the coccolithophore nannoflora. Top—red: coccolith mass of E. huxleyi, G. ericsonii, and G. muellerae. Bottom—blue: relative abundance of G. oceanica. Colored lines represent the LOESS function and the dotted lines represent polynomial of fourth order to depict the long-term tendencies. Vertical colored bars are synchronous events common to the two series
Fig. 7 Comparison of the abundance of G. oceanica and SST for the last 700 years. Top: Records of %G. oceanica. Bottom: SST (UK37 from Zhao et al. (2000)). Both records are from the same position in the Santa Barbara Basin. Colored lines represent the LOESS smoothing function for the two series. Vertical bands are long-term increases of temperature detected by the two proxies
scale. Singular spectrum analysis (SSA) (Vautard and
Ghill
1989) is performed on the composite record
COCOC to determine the relative importance in the
total variance of those differences of frequency
components. The time series is decomposed in forty
independent principal components (PC). The first
PC (PC1) contains 46.3% of the total variance; PC2,
8.9%; PC3, 5.2%; and all the other PCs (4 to 40)
together, 39.6%. The first three PCs capture more
than half of the variance as it is shown in Fig.
12.
PC2 appears to fluctuate at about 200 years
periodicity and PC3 with pseudoperiods centered
on 100 years. Higher important frequencies are
centered on period of 30 years (Fig.
10). The
strongest PDO+ events and in a lesser extent the
strongest PDO− events appear during times of high
values of the PC2 (Fig.
11). This indicates that the
centennial variability acts also as a modulator of the
PDO variability and/or that during an increase of
centennial mean of PDO, the negative PDO events
remain strong. In other words, the amplitude of
PDO cycle increases during centennial
“warm”
events.
Such a centennial variability is observed in the
derivative
δ
18O from Pyramid Lake, Nevada,
(Benson et al.
2002) and is characteristic of drought
occurrences over western USA. The long-term
tendency is also similar between the records
(see polynomials in Fig.
12). Each of the 17 episodes
of drought occurring with a pseudoperiod of 150 year
described in Benson et al. (2002) for the last
2700 years corresponds to decreases of %GEO and
CM (Fig.
12) (albeit a shift of 50 years probably due
to difference in record chronology). This relation
may be interpreted as a weakening of the DC,
presumably related to La Niña-like conditions.
Sustained La Niña-like conditions and associated
changes in PDO appear to drive the drought periods
over the western USA.
PDO is a complex combination of different
dynamical parameters (Newman et al.
2016). The
different published PDO proxies (e.g., Benson et al.
2003; MacDonald and Case
2005, COCOC) are
responding mainly to one of the dynamical
parameter and do not necessarily englobe the entire
complexity of PDO. This explains some differences
existing between all these PDO reconstructions.
Cross spectral analysis of %GEO versus CM reveals
pseudoperiodicity around 100 and 200 years (Fig.
9).
Those records are highly coherent with each other
and with that of
δ
18O from Pyramid Lake, pointing
to the highest coherency (>95%) at frequencies of 1/
213, 1/193, and 1/96 years
−1. These frequencies are
also very similar to those commonly cited as de
0 0.2 0.4 0.6 0.8 1 -3 -2 -1 0 1 2 3 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Cross Blackman Tukey (SST vs %G.oceanica) Coherency Phase (rad.) Frequency (1/year) 118 years 36 years 24 years 95% Confidence level BW 3y 10y -10y -7y -4.6y -3.5y 22 years 0.5y 2.2y In phase
Fig. 8 Cross spectral analysis (Blackman-Tukey) between the 700 year record of SST (Zhao et al. 2000) and %G. oceanica in the Santa Barbara Basin. No-Zero coherence at 95% is higher than a confidence level of 0.665 (red horizontal line). The bandwidth is 0.0046 (red horizontal bar marked BW). Lengths of significant periods are indicated in the graph. For those, the phase between the two series is indicated by vertical blue lines representing the phase error bar at 80% with the upper and lower limits expressed in years. The horizontal blue line is the zero phase. For positive phase value, SST is leading and for negative phase values, %G. oceanica is leading
0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 10 100 1000
Cross Blackman Tukey Coc Mass vs %G.oceanica)
Coherency Period (year) 95%CL 364y 204y 31y 22y 59y 119y 89y
Fig. 9 Cross spectral analysis (Blackman-Tukey) between the 2700 year records of coccolith mass of (Gephyrocapsa ericsonii, G. muelerae, E. huxleyi) and %G. oceanica in the Santa Barbara Basin. No-Zero coherence at 95% is higher than a confidence level of 0.705 (blue horizontal line). The bandwidth is 0.00093. Lengths of significant periods are indicated in the graph
Vries or Suess (~1/200 year
−1) and Geisberg
(1/83 year
−1) cycles found in cosmogenic (
14C and
10Be) records (e.g., Emile-Geay et al.
2007; Neftel
et al.
1981; Ogurtsov et al.
2002; Suess
1980). Similar
cycles are also found in records of the PDO (Benson
et al.
2003) and of the Pacific-North American
teleconnection pattern (PNA) (Liu et al.
2014;
Steinman et al.
2012). This similarity of the
variability points to an influence of solar radiation
on the ENSO. Mann et al. (2005) studied the
importance of volcanic activity and solar irradiance
on the ENSO dynamics for the last 1000 years by
using Zebiak and Cane (1987) model of the tropical
Pacific coupled ocean–atmosphere system. In this
model, ENSO reacts to solar irradiance due to a
zonal asymmetry in the response of the tropical
pa-cific: a heating due to higher irradiance would cool
the East Pacific, inducing a La Niña-like climatic
system.
Such climatic variability appears to be coherent with
the amount of heat received by the Earth from the
sun: an apparent relation exists between these data
and those of the total solar irradiance anomalies
(TSIa). Phases of La Niña-like and associated
drought conditions over western USA coincide with
decrease or negative values of TSIa. Direct solar
irradiance including also volcanic activity is
controlling ENSO (Liu et al.
2015) by playing a role
in the energy received at the ocean level: the
influence of both solar irradiance and volcanic
activity on ENSO has been tested by numerical
simulations (Mann et al.
2005). The results of those
simulations have been compared visually to the
composite of the coccolithophore records. This
indicates that the ENSO simulation with the solar
irradiance as sole forcing exhibits synchronous
events with coccolithophore record (COCOC)
(Fig.
13); the ENSO simulation using both solar
irradiance and volcanic activity hardly shows any
similarity with coccolithophore records (Fig.
13).
1985 1918 1880 1804 1750 1696 1582 1489 1372 1321 1180 1135 1084 1036 877 829 775 724 675 564 495 423 372 300 213 115 33 3 -53 -128 -210 -295 -372 -414 -458 -518 -571 -668 COCOC 1.0 0.5 0 0.5 1.0 1.5 SSA 0.4 0.2 0 0.2 Year (CE) 1000 0 1000 2000 0 2 4 6 0 0.05 PDO+ El Niño PDO-La Niña Frequency (Cycle/year) 0 0.5 1.0 1.5 0 0.05 200 years 100 years 30 years MTM power MTM power
Fig. 10 Variability of the COCOC (composite coccolith proxy) during the last 2700 years in the Santa Barbara Basin. Bottom left panel shows the COCOC record in red and blue color, the limit between red and blue is a detrended COCOC record by the 1st PC of a SSA (Vautard and Ghill 1989) and the 2nd PC of a SSA (the embedding dimension is 40) in black dotted line. Top left panel represents the 2nd (red) and 3rd (blue) PCs of the SSA. The dates of each minima (blue text) and maxima (red text) of the 2nd PC are given. Right panels represent the spectral analysis performed with the Multi-Taper Method (Thomson 1982) of the 2nd PC (red in top panel), 3rd PC (blue), and the COCOC record detrended with the 1st PC (red in the bottom panel). The principal period is given in year
COCOC SSA 1.0 0.5 0 0.5 1.0 1.5 2.0 Year (CE) 500 0 500 1000 1500 2000
Fig. 11 Modulation of the multi-decadal amplitude of COCOC by its centennial to bicentennial scale variability: The red and blue lines represent all the PCs higher than 4 (e.g., mutli-decadal amplitude), and the dotted black line the two PC (centennial to bicentennial variability)
Fig. 12 Two thousand and seven hundred-year records in the top panel and in red, the smoothed (10 year) record ofδ18O record in core PLC97-1 from Pyramid Lake (Benson et al. 2002) shifted (arbitrarily) by +50 years, and in the bottom panel and in blue, the COCOC record. The blue solid line represents the LOESS function. The colored dotted lines represent polynomial of fourth order to depict the long-term tendencies. Vertical colored bars are events common to the two series
Fig. 13 One thousand-year records in the top panel and in red, the COCOC record, and in the bottom panel and in blue, the smoothed (40 year) record of the simulations (ensemble of 100 realizations with the Zebiak and Cane model) of NINO3 to solar radiative forcing in blue and to volcanic and solar radiative forcing (black dotted line) adapted from Mann et al. (2005). The colored solid lines represent the LOESS functions of those records. Vertical colored bars are events common to the two series
This could be indicative that solar activity is
responsible in a large part of the ENSO and PDO
dynamics and that volcanic activity as limited
impact on PDO/ENSO dynamics. This is even
further demonstrated by the lack of synchronism
between the timing of the large PDO events found
in the COCOC record and the timing of the major
volcanic eruptions occurred during the last
2500 years described by Sigl et al. (2015). This
would explain why there is stable centennial
variability similar to that of the solar cycle
(knowing that volcanic activity should not be cyclic).
The persistence of quasi-bicentennial cycle during
the entire Holocene in the North America has been
recently described elsewhere (Liu et al.
2014) and
confirms the permanence of the centennial to
bicentennial dynamics in the eastern Pacific and
North America.
Conclusions
We presented here two 2700 years' long records from the
Santa Barbara Basin of ENSO/PDO proxies based on
coc-colithophores: one resulting from the relative abundance
in the assemblage of one warm species Gephyrocapsa
oceanica and the other from the degree of calcification of
a group of three abundant species (Emiliania huxleyi, G.
ericsonii, G. muellerae). The first proxy appears to be
related primarily to SST changes and to ENSO, and the
second proxy is more related to the dynamics of the
upwelling and on PDO. Although the two proxies are
independent, they show similar dynamics:
1. A general decrease (in abundance and mass) over
the last millennia until 300 years ago. Since then, the
values increase. This recent increase is particularly
pronounced for the mass values that show the
highest in the 2700 record in the last 30 years. This
general trend is in accordance with the general
decrease of SST in the ocean and in particular in the
coast of California (McGregor et al.
2015). The
impact of ocean acidification in the most recent part
of the record may be limited because the relatively
old waters upwelled in this area delay the drop of
pH by 50 years (Feely et al.
2008).
2. In addition to this long-term variation, there is a
strong variability at multi-decadal (periods of 23 and
39 years), centennial, and bicentennial that are
typical of ENSO and PDO in that region. The
multi-decadal amplitude is modulated by the centennial/
bicentennial variability, implying that both phases
(negative and positive) of the PDO are increased
during high mean COCOC value events at
centennial to bicentennial scale.
The presence in those records of de Vries or Suess
(~1/200 year
−1) and Geisberg (1/83 year
−1) cycles that
are associated to solar radiation is indicative of the
radiative forcing as an important factor of climatic
vari-ability in the eastern Pacific regions.
Abbreviations
AL:Aleutian Low; CC: California Current; CCS: California Current System; CM: Coccolith mass; COCOC: Composite coccoliths records; DC: Davidson Current; ENSO: El Niño Southern Oscillation; NPH: North Pacific High; PDO: Pacific Decadal Oscillation; SBB: Santa Barbara Basin
Acknowledgements
We thank the IMAGES program, IPEV, and the crew of the RV Marion-Dufresne for retrieving the core MD02-2503. LB gratefully acknowledges the invitation and support by Pr Masanobu Yamamoto to participate to the INQUA 2015 symposium held in Nagoya, Japan.
Funding
We thank the Agence Nationale de la Recherche for its financial support to LB under projects ANR‐12-BS06‐0007–CALHIS and JPI Blemont project ANR-15-JCLI-0003-05–PACMEDY. This work is a contribution to the EU FP7 project MedSeA (grant agreement no. 265103).
Authors’ contributions
LB proposed the topic. MG carried out the experimental study. LB and MG interpreted the data. LB wrote the first drafts of the manuscript and both approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Publisher
’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Author details 1
Aix Marseille University, CNRS, IRD, Collège de France, CEREGE, Avenue Louis Philibert, BP8013545 Aix-en-Provence, Cedex 04, France.2Institute of
Environmental Science and Technology, Autonomous University of Barcelona (UAB), Bellaterra 08193, Spain.
Received: 13 November 2016 Accepted: 9 March 2017
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